Vehicles using high-efficiency internal combustion engines often incorporate an auxiliary heater. These engines, due to their high efficiency, produce very little waste heat that is available for the heating system of the motor vehicle. The small amount of thermal energy that results, if used alone to heat the passenger compartment, is often uncomfortable for the vehicle occupant. Therefore, vehicles may contain a heat exchanger in the exhaust gas line of the vehicle so that heat from the exhaust gas flow can be used to heat the interior of the vehicle.
This type of system generally has a flow route passing through the heat exchanger and a bypass that runs parallel to the flow route. In this manner, the heat exchanger can be switched off. For example, exhaust gas may be directed through the bypass instead of through the flow route immediately after the internal combustion engine is started until a catalytic converter arranged in the exhaust gas line is to be brought to its operating temperature. If the exhaust gas were allowed to flow through the heat exchanger instead of the bypass, it would take longer for the catalytic converter to reach its operating temperature because the heat exchanger has a large thermal capacity and would therefore absorb heat meant to reach the catalytic converter.
Problems caused by thermal expansion among various component parts occurs in virtually all heat exchangers disposed in the exhaust gas line of a vehicle. For one thing, the component parts are exposed to temperature differentials of many hundreds of degrees Celsius. Moreover, there is often a steep temperature gradient between the various component parts even when the operating state is constant. Ideally, the various thermal expansions are reliably absorbed over a multiplicity of operating cycles and prevent leakage from occurring in the exhaust gas line, but as a practical matter this does not occur in currently known heat exchanger assembly designs. Thus, the differing thermal expansions of the various components causes stress among the components, potentially causing leakage.
There is a desire for a simple heat-exchanger housing design that can be manufactured in a cost-effective manner while simultaneously permitting the various thermal expansions of the various component parts without causing any leakage.